This application claims priority from United Kingdom Serial No. 9906322.4 filed Mar. 19, 1999.
The present invention pertains to a respirator that provides a forced flow of filtered air to the wearer and that can alert the wearer when suction generated by the air flow falls below a predetermined value.
One of the common purposes of a respirator is to prevent contaminants from entering a wearer""s respiratory system. A respirator typically comprises a head piece that is shaped to form a breathing zone around at least the nose and mouth of the wearer. In some respirators, the wearer""s breathing action causes air to be drawn into the breathing zone through a filter. Other respirators, however, provide a forced flow of filtered air to the breathing zone to relieve the wearer of the need to inhale against the resistance of a filter and to ensure that any leakage in the respirator is outwardsxe2x80x94that is, away from the breathing zone rather than into it.
Respirators that use a forced flow are preferred in certain working environments, particularly those that are physically demanding on the wearer and those where the wearer is likely to benefit from the cooling effect of air flowing through the breathing zone.
A forced flow of air into the breathing zone of a respirator may be generated by a fan or by a blower which, together with its power source, may be carried by the respirator wearer. This kind of system is known as a powered air system. Alternatively, the forced flow of air may be obtained from a source of compressed air, which may be either fixed or portable. A system that uses compressed air is commonly known as a supplied air system.
Examples of respirators that provide a forced flow of filtered air to the wearer are described in U.S. Pat. Nos. 4,133,308, 4,136,688, 4,280,491 and 4,462,399, and in GB-A 2,032,284. Forced flow respirators can have an indicator device that is capable of warning the wearer when air flow into the breathing zone falls below a safe level. Regulations are increasingly being introduced to make these indicator devices compulsory; see, for example, the new European standard EN 12941. Examples of indicator devices that have previously been proposed are described in DE-A-30 32 371, GB-A 2,130,893, U.S. Pat. No. 4,765,326, and in EP-A-0 349 191 and 0 602 847. It nevertheless remains desirable to provide an indicator device that will not add substantially to the cost of a respirator and that will function reliably without substantially affecting the forced air flow into the respirator breathing zone.
The present invention provides a respirator that provides a forced flow of filtered air to a wearer, the respirator comprises:
a head piece that is shaped to form a breathing zone around at least the nose and mouth of the wearer;
an air flow passage that carries a forced flow of air to the breathing zone, the passage having a constricted portion that contains a flow detecting orifice such that the forced flow of air generates suction at the flow-detecting orifice, the degree of suction being related to the air flow rate in the passage; and
a pressure-responsive indicator device that is in fluid communication with the flow-detecting orifice and that is operable to alert the wearer if the suction generated by the air flow through the passage falls below a predetermined value.
As used herein, the term xe2x80x9cairxe2x80x9d includes breathable gases.